Low-altitude remote sensing of volcanoes using an unmanned autonomous helicopter: an example of aeromagnetic observation at Izu-Oshima volcano, Japan

The results of aeromagnetic observations at Izu-Oshima, Japan using an unmanned autonomous helicopter are reported. A practical observation system was assembled, adopting a bird-type magnetometer installation, and dense observations of the northern half of the caldera area including the central cone were made from a very low altitude. In the detailed magnetization intensity mapping deduced from the collected data, low magnetization intensity at the vent and three rows of high magnetization intensity on the caldera floor were found. The former is interpreted as the presence of high-temperature materials, such as magma or hot rock, or vacant space in the conduit. The latter is considered to be due to solidified dykes. Low magnetization intensity suggesting a magma body (or subsidiary magma chamber) was not detected below the caldera floor. The observation results confirmed that aeromagnetic observation using an unmanned autonomous helicopter had sufficient performance for volcanic observations, and could also be utilized as a low-altitude platform for other sensors.